feat: query devtools, error boundary, real-time P&L polling, and funding countdown

[ijeoma270]

Fixes #63
Fixes #64
Fixes #65
Fixes #66

What changed

#63 — TanStack Query DevTools in dev mode

• Added @tanstack/react-query-devtools to devDependencies in apps/web/package.json
• QueryProvider conditionally renders <ReactQueryDevtools initialIsOpen={false} /> behind import.meta.env.DEV; Vite tree-shakes it from production bundles entirely

#64 — Global error boundary + query error fallback UI

• QueryProvider now creates a QueryCache with an onError callback: logs to console.error in dev, fires a red Sonner toast with parseSorobanError() message for user-visible failures; auth-related errors (401/403/unauthorized/unauthenticated) are silently skipped
• New ErrorPage component (app/error-page.tsx) — renders a centred "Something went wrong" message with a Reload button
• ErrorBoundary class component added to AppProviders — wraps the whole tree, calls getDerivedStateFromError / componentDidCatch, renders <ErrorPage onReset={...} /> on failure and resets state when the user clicks Reload

#65 — Real-time P&L polling for open positions

• usePositions: refetchInterval lowered from 15 000 → 5 000 ms so P&L, liquidation price, and funding debt update roughly every 5 s
• Added refetchIntervalInBackground: false — network requests pause automatically when the tab is hidden; disconnecting the wallet already stops polling via enabled: !!account

#66 — Live funding countdown timer in PositionsList

• New useFundingRate hook (hooks/useFundingRate.ts) returns { ratePerHour, nextEpochTs } computed from the standard 8-hour funding epoch schedule; refreshes every 60 s
• Added fundingRate key to the central queryKeys factory
• useFundingCountdown (private hook inside PositionsList) runs a setInterval every second, diffs Date.now() against nextEpochTs, and formats remaining time as "Xh Xm" or "Xm"; the interval is cleaned up via the useEffect return
• PositionsList gains a Next Funding column visible on all open-position rows

How to test

#63 — run bun dev, open the app, a floating ⚛ button appears in the bottom-right corner in dev mode.

#64 — throw inside any child component (throw new Error("test")); the app renders the reload page. For query errors, mock a failing query; a red toast appears within seconds.

#65 — open the Trade page with a connected wallet and watch the P&L column refresh roughly every 5 s. Switch to another browser tab and confirm no network requests fire (DevTools → Network).

#66 — open the Trade page with positions loaded; the Next Funding column counts down in real-time (updates every second). Verify it resets after each 8-hour epoch.

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